Well to be honest, i really cannot say exactly how much the price of bitcoin will fall. But looking at the statistics and reading some speculations from a person's mouth to another,  the approximation I have in mind is about 1000+-2000+ decrease in bitcoin prices after a few days or weeks from the fork date. But bitcoin's price will probably just rise again on the later weeks and probably even reach lots of peaks. So there's really not that much to worry about.